He has a record within Westminster as a radical reformer but also a divisive character, once described as a "career psychopath" by David Cameron.

However, since Mr Johnson appointed him, he is considered to be one of the most powerful people in Downing Street.

In the early 2000s, Mr Cummings served as director of strategy for the Conservative Party.

He left the role and later branded then Tory leader Iain Duncan Smith as "incompetent", adding he would be a "worse prime minister than Tony Blair and must be replaced".

He later campaigned against Labour's proposal for an elected regional assembly in the North East, before going on to work as a special adviser for Michael Gove.

When the Conservatives were elected to power as part of the coalition government in 2010, Mr Cummings' employment at Mr Gove's Department for Education was banned by the then director of communications Andy Coulson.

After Mr Coulson resigned following allegations of phone hacking at the now defunct News of the World while he was editor, Mr Cummings became Mr Gove's chief of staff.

Allegations were made by civil servants of an "us-and-them aggressive, intimidating culture" under the pair, before Mr Cummings left this role in 2013 in order to open a new free school.

Then prime minister Mr Cameron is later reported to have described Mr Cummings as a "career psychopath".

Ahead of the 2016 EU referendum, Mr Cummings joined the Vote Leave campaign but soon clashed with eurosceptic Tory MPs.

He survived an attempt to oust him from the campaign and was later credited as one of the most influential figures behind Vote Leave's success under its "Take Back Control" slogan.

Benedict Cumberbatch portrayed Mr Cummings in a Channel 4 drama of the 2016 EU referendum campaign which focused on his role in covering a red bus with the disputed £350m a week figure, arguing the cash could be used to fund the NHS.

Mr Cummings, a hate figure for many pro-EU politicians, said the £350m/NHS argument was "necessary to win" the campaign.

Last year, Mr Cummings refused to appear before the House of Commons' digital, culture, media and sport committee as part of their fake news inquiry.

He was called to appear to respond to "allegations made against the Vote Leave campaign" during the inquiry and to "clarify allegations about the unlawful coordination of EU referendum campaigns".

Mr Cummings was a fierce critic of Theresa May's handling of Brexit, saying her plan for leaving the EU was "unacceptable bulls***" and attacked a "truck load of c*** ideas" from government ministers, who he called "morons".

He also argued against the government's decision to trigger the Article 50 notification to leave the EU so soon after the 2016 referendum, calling it an "historic unforgivable blunder".

In 2017, he branded then Brexit secretary David Davis "thick as mince, lazy as a toad, and vain as Narcissus".

Despite being the former chief of the Vote Leave campaign, Mr Cummings has not shied from laying into the European Research Group of Tory Brexiteer MPs.

He claimed the collective had been "useful idiots" for Remain.

Referring to the group, led by Jacob Rees-Mogg, he wrote in a blog: "You should be treated like a metastasising tumour and excised from the UK body politic."

Mr Johnson appointed Mr Cummings as senior adviser at Number 10 when he became prime minister in the summer of 2019.

The election victory in December 2019 gave Mr Johnson the political capital he needed to take bold decisions.

Mr Cummings soon set to work on his ambition to reshape Whitehall, issuing a recruitment call for data scientists, economists and "weirdos and misfits with odd skills" to shake up the Civil Service.